accumulate_iter_merge_sort.cpp

template<typename ForwardIterator>
void stable_sort_forward(ForwardIterator first, ForwardIterator last)
{
    using Range = std::pair<ForwardIterator, ForwardIterator>;
    using Counter = binary_counter<merger<ForwardIterator>, Range>;
  
    Counter c { merger<ForwardIterator>{}, { last, last } };
    accumulate_iter(first, last, &c,
                    [](auto c, auto it) {
                        c->add({it, std::next(it)});
                        return c;
                    })->reduce();
}